It is well known in the art to employ organic polymers dissolved or dispersed in organic solvents in forming coatings. The formation of coatings using such solvents or dispersions involves the removal of large quantities of organic solvents and, particularly in recent years, such solvent removal has been considered undesirable from ecological and environmental considerations. Accordingly, there has been an increased interest in coatings compositions wherein the organic polymer is dissolved or dispersed in a medium consisting primarily of water. Many such aqueous coating compositions, including those containing amine salts of carboxy groups for increased water-dispersibility, have been unacceptable because reagents introduced during their preparation have deleterious effects on the final coating. For example, vinyl chloride resin latices made by emulsion polymerization require the use of surfactants which remain in the final coating and impart poor water resistance (blush) to the coating. Film-forming polymers made by condensation polymerization, such as epoxy resins, have been rendered water-dispersible by grafting carboxyl-containing monomers thereto using a peroxide catalyst. While these polymers provide satisfactory coatings, the peroxide catalysts used in this process are relatively hazardous materials to store and handle. Another method for producing water-dispersible coating compositions is based on a transesterification reaction between equimolar reaction products, the first of which is a copolymer of a vinyl ester of an alpha-branched acid, styrene, hydroxyalkylester and an alkyl ester of an alpha-beta ethylenically unsaturated acid and the second of which reaction products is in turn a reaction product of trimellitic anhydride and a glycidyl ester of an alpha-branched acid. While water-dispersible coating compositions are obtained from these latter reaction products, the multiplicity of starting materials makes for a difficult preparative process.
It is, therefore, an object of this invention to provide a coating composition which is simple to prepare and economical and which is readily convertible to a water-dispersible composition by neutralization.
It is a further object of this invention to prepare a water-dispersible coating composition which does not present gelling problems during its preparation.
It is a still further object of this invention to prepare a water-dispersible coating composition which is shelf-stable.
Other objects of this invention will become apparent to those skilled in the art upon a further reading of this following specification.